95d6e70deaf83720c3959ba04dd80100.jpeThe obliquebanded leafroller has displaced pandemis as the primary leafroller pest in north central Washington.

Mike Doerr, entomologist with Washington State University in Wenatchee, said that several years ago, more than 80 percent of the leafrollers found in the region’s orchards were pandemis, but that species is not found very much any more.

Whereas pandemis is limited to apples, the obliquebanded leafroller has a broad host range, and a slightly different life cycle. The obliquebanded leafroller emerges later in the spring, which means that applications of Lorsban (chlorpyrifos) at the delayed-dormant stage will not impact it as much
as they do pandemis. A delayed-dormant Lorsban treatment may not be enough to control even one generation of the pest.

Also, the obliquebanded leafroller can be found throughout the canopy, whereas pandemis is found mainly on the shoot tips. So, sprays targeted at the tops of the tree might miss obliquebanded leafrollers that are lower in the canopy.

In addition, the obliquebanded leafroller is less sensitive to pesticides, and pandemis is sensitive to a virus that is similar to the granulosis virus of codling moth.

Several insect growth regulators are available to control leafrollers. Esteem (pyriproxyfen) is a juvenile hormone mimic that prevents the insects from developing past the pupal stage. Intrepid (methoxyfenozide) and Rimon (novaluron) are chitin inhibitors that prevent the insects from molting. The growth regulators do not have immediate effect, and the larvae will continue to feed after exposure. To be effective, the products must be consumed within five days of application because of the growth of the foliage, Doerr said.

“These new insecticides have to be consumed to be effective,” Doerr said. “Spray coverage is the most important thing. Spray coverage and timing of the leafroller spray is more important than the product you choose.”

However, the insect has developed resistance to some pesticides, he said. There was evidence of resistance to Intrepid even before it was registered in 2001, although the resistance level hasn’t changed over time. The insect has also developed resistance to Success (spinosad).